In a network (called an “MPLS network”, below) which uses MPLS (multi protocol label switching) (see Non-Patent Document 1), an “MPLS TE” (traffic engineering) technique (see Non-Patent Document 2) is used for controlling a large amount of traffic.
In the MPLS TE technique, a plurality of parallel links are connected between nodes, so as to handle a large amount of traffic. In order to efficiently use the links, it is necessary to equally distribute “MPLS TE LSPs (label switched paths)” (called “MPLS paths”, and see Non-Patent Document 2) for the frequency band and the number of the paths, where the MPLS paths are arranged along links provided between the start node (as the start point of the relevant communication) and the end node.
When setting MPLS paths by using reserved bands, it is possible to equally distribute the MPLS paths, which are arranged along links between the relevant nodes, by using already-established techniques (see Non-Patent Documents 2 and 6).
However, when setting MPLS paths while there is no reserved band at present, if there is an ECMP (equal cost multi path) (see Non-Patent Document 3) in an MPLS network, then load distribution cannot be performed between the relevant nodes. In this case, a problem (e.g., path concentration at a specific link) occurs, which obstructs efficient establishment of MPLS paths.
Conventionally, systems disclosed in Non-Patent Documents 4 and 5 are implemented.
In addition, computation of MPLS paths is performed at the start node, by using LSA (link state advertisement) data (see Non-Patent Documents 3 and 6) defined in OSPF (open shortest path fast) protocol (see Non-Patent Document 3).
On the other hand, in order to distribute MPLS paths along links between the relevant nodes, it is proposed that the number of the MPLS paths be communicated to relevant systems, by using the OSPF protocol (see Non-Patent Document 7). However, a specific method of computing the MPLS paths has not been shown.
Non-Patent Document 1: E. Rosen, A. Viswanathan, R. Callon, “Multiprotocol Label Switching Architecture”, IETF RFC3031, January, 2001.
Non-Patent Document 2: D. Awduche, et al., “RSVP-TE: Extensions to RSVP for LSP Tunnels”, IETF RFC3209, December, 2001.
Non-Patent Document 3: J. Moy, “OSPF version 2”, IETF RFC2328, April, 1998.
Non-Patent Document 4: “How CSPF Selects a Path”, retrieved from the Internet on Mar. 7, 2007.
Non-Patent Document 5: E. Osborne, A. Simha, “Traffic Engineering with MPLS”, pp. 119-124, Cisco Press, 2003.
Non-Patent Document 6: D. Katz, et al., “Traffic Engineering (TE) Extensions to OSPF Version 2”, IETF RFC 3630, September, 2003.
Non-Patent Document 7: J.-P. Vasseur, M. Mayer, K. Kumaki and A. Bonda, “A Link-Type sub-TLV to convey the number of Traffic Engineering Label Switch Paths signalled across a link”, IETF Internet draft, June, 2006. (draft-ietf-mpls-number-0-bw-te-lsps-05.txt)
A conventional technique disclosed in Non-Patent Documents 4 and 5 has a problem, which will be explained with reference to a network shown in FIG. 7.
In the network shown in FIG. 7, links E-F, G-H, and I-J are provided in parallel between core routers R3 and R4. In addition, a link A-B is provided between an edge router R1 and the core router R3; a link C-D is provided between an edge router R2 and the core router R3; a link K-L is provided between an edge router R5 and the core router R4; and a link M-N is provided between an edge router R6 and the core router R4.
In the conventional technique, when establishing a plurality of MPLS paths between the edge router R1 (the start node) and the edge router R5 (the end node), many paths are concentrated at the link E-F between the core routers R3 and R4, or paths are not equally distributed among the links E-F, G-H, and I-J.
Therefore, even when a plurality of links is established between the relevant nodes so as to control a large amount of traffic, paths are concentrated to a specific link, and thus the network works (i) without using the other links, or (ii) while usage rates of each link are not equal. Therefore, the links cannot be sufficiently efficiently used.